Fan shroud and/or fan blade assembly

ABSTRACT

Briefly, embodiments of a fan for moving a volume of compressible fluid from an upstream side to a downstream side may comprise a vortex circulation channel formed within a shroud substantially surrounding the blades of the fan. As a portion of one or more blades of the fan moves within the vortex circulation channel, a vortex that is formed and confined within the channel may reduce formation of a vortex within the fan working area, thereby bringing about an increase in a volume of the compressible fluid capable of being moved by the fan. In an embodiment, a fin or other protrusion disposed on a tip portion of a blade may additionally increase flow of a compressible fluid through a fan. In an embodiment, use of a wraparound leading edge of a fan shroud may bring about further increases in volume of compressible fluid flow.

BACKGROUND 1. Field

This disclosure relates to equipment that may be utilized to move acompressible fluid, such as portable fans, and, more particularly, to areduced-footprint high-volume fan shroud and blade assembly.

2. Information

At times, a fan may be utilized to move a compressible fluid, such asambient air, for example, to bring about ventilation, forced-aircooling, heating, drying, fumigating, cleaning, and so forth. In manyapplications, a fan may consume a large external footprint to bringabout movement of a volume of air, for example, via the fan's workingarea. In turn, a large external footprint may increase overalldimensions of the fan, which may limit portability of the fan.Accordingly, improving a fan's throughput and/or reducing a fan'sexternal footprint may represent an area of continued interest and/ordevelopment.

BRIEF DESCRIPTION OF DRAWINGS

Claimed subject matter is particularly pointed out and/or distinctlyclaimed in the concluding portion of the specification. However, both asto organization and/or method of operation, together with objects,features, and/or advantages thereof, claimed subject matter may beunderstood by reference to the following detailed description if readwith the accompanying drawings in which:

FIG. 1 is a perspective view of an example axial fan, wherein aplurality of fan blades rotate in a plane within a volume substantiallysurrounded by a fan shroud;

FIG. 2 is a schematic view of an axial fan, showing fan blades rotatingin a plane within a volume substantially surrounded by a shroud;

FIG. 3 is a schematic view of an example axial fan, showing fan bladesrotating in a plane within a volume substantially surrounded by ashroud, according to an embodiment;

FIG. 4 is a schematic view of an example axial fan showing fan bladesrotating in a plane within a volume substantially surrounded by a shroudaccording to an embodiment;

FIGS. 5A-5D illustrate one or more fan blades that may include afin-shaped or other type of projection according to embodiments;

FIG. 6A is a schematic view showing fan blades rotating in a planewithin a volume substantially surrounded by a shroud;

FIG. 6B is a schematic view of a portion of an axial fan within shroudhaving a wraparound forward edge according to an embodiment;

FIGS. 6C-6D are schematic views of inlet vanes, such as those shown inFIG. 6B, according to embodiments;

FIGS. 6E-6F are schematic views of inlet vanes showing an increase infan working area according to an embodiment;

FIG. 7A is a schematic diagram showing velocity gradients at variouspoints along an aerodynamic surface of a fan blade;

FIG. 7B is a schematic diagram showing velocity gradients at variouspoints along an aerodynamic surface of a primary blade responsive to apresence of secondary blade according to an embodiment;

FIG. 7C is a schematic diagram showing various dimensions of a primaryblade and a secondary blade according to an embodiment;

FIG. 7D is a schematic diagram showing possible orientation angles ofsecondary blade relative to a chord line of a primary blade according toan embodiment; and

FIG. 8A is a schematic diagram showing cross section of a fan shroud,vortex pocket, and arc-shaped inlet vanes according to an embodiment;

FIG. 8B is a schematic diagram showing a primary and secondary blade,wherein the primary blade comprises an increasing pitch toward the bladehub, according to an embodiment; and

FIG. 8C provides a diagram showing a numerical example utilized indetermining, or at least estimating, blade pitch of sections of theprimary and secondary blades of FIG. 8B.

Reference is made in the following detailed description to accompanyingdrawings, which form a part hereof, wherein like numerals may designatelike parts throughout the figures to indicate corresponding and/oranalogous components. It will be appreciated that components illustratedin the figures have not necessarily been drawn to scale, such as forsimplicity and/or clarity of illustration. For example, dimensions ofsome components may be exaggerated relative to other components.Further, it is to be understood that other embodiments may be utilized.Furthermore, structural and/or other changes may be made withoutdeparting from claimed subject matter.

DETAILED DESCRIPTION

Reference throughout this specification to “one example,” “one feature,”“one embodiment,” “an example,” “a feature,” “an implementation,” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the feature, example, orembodiment is included in at least one feature, example, or embodimentof claimed subject matter. Thus, appearances of the phrase “in oneexample,” “an example,” “in one implementation,” “an implementation,”“an embodiment,” or “in one embodiment” in various places throughoutthis specification are not necessarily all referring to the samefeature, example, or embodiment. Particular features, structures, orcharacteristics may be combined in one or more examples, features, orembodiments.

As previously mentioned herein, a fan may be utilized to move ambientair, for example, in various applications such as ventilation,forced-air cooling, heating, drying, fumigating, cleaning, and so forth.In many applications, a fan may consume a large external footprint so asto be capable of moving a significant volume of ambient air, or othertype of compressible fluid, for example. However, responsive to a fanconsuming a large external footprint, portability, performance, andstorage volume of a fan may be negatively impacted. Thus, reducingphysical size and improving throughput of a fan, such as via improvedfan blade and/or fan shroud design, for example, may represent acontinued area of interest.

Particular types of fans may comprise one or more blades, rotating in aplane, and disposed or situated within a shroud, such as acylindrically-shaped, stationary shroud, as one possible example. Use ofa cylindrically-shaped, stationary shroud may operate to confine and todirect a volume of a compressible fluid, such as ambient air, forexample, from an upstream side of the blades of the fan, which maycorrespond to a region towards the front of the fan blades, to adownstream side, which may correspond to a region towards the rear ofthe fan blades. However, in many instances, as one or more fan bladesrotate in a plane about a central axis, thereby driving a compressiblefluid from an upstream side of the volume enclosed by acylindrically-shaped shroud to a downstream side, pressure at thedownstream side may increase relative to pressure at the upstream side.Accordingly, a portion of the volume of the compressible fluid may beredirected towards an opposite direction, such as from a downstream sideof the fan blades towards an upstream side of the fan blades. In someinstances, compressible fluid flow in the opposite direction may belocalized to within a gap-like region that defines a spacing between atip portion of the one or more rotating blades and the inner surface ofthe cylindrically-shaped shroud. In many applications, fluid flow from adownstream side of a volume enclosed by a cylindrically-shaped shroud,through a gap-like region or spacing between a tip portion of a blade,and into an upstream side of the volume may undesirably impact a fan'scapability to move large volumes of compressible fluid.

As the compressible fluid flows in the opposite direction (e.g., adownstream side towards an upstream side), such as through a gap-likeregion or spacing between a tip portion of a rotating blade and theinner surface of a cylindrically-shaped shroud, a portion of theoppositely-directed fluid may collide with the compressible fluidflowing from the upstream side towards the downstream side. In responseto such colliding, at least a portion of the oppositely directed fluidmay be redirected towards the center of the cylindrically-shaped volumeconfined by the cylindrically-shaped, stationary shroud. Responsive toredirection of the fluid towards the center of the cylindrically-shapedvolume, the direction of the opposing fluid may be further modified soas to begin flowing from the upstream side of the volume enclosed by thecylindrically-shaped shroud towards the downstream side. As the fluidencounters higher pressure at the downstream side of thecylindrically-shaped volume, a portion of the fluid may be deflectedtowards the perimeter of the volume, where the fluid may again bepermitted to flow through a gap-like region or spacing between a tipportion of a blade and the inner surface of the cylindrically-shapedshroud.

Under certain circumstances, such fluid circulation, which may beginwith flow of a compressible fluid from a downstream side to an upstreamside, followed by redirection of the flow toward a center portion of thecylindrically-shaped volume, towards the downstream side, and (again) ina direction towards the upstream side, may be referred to as a “vortex.”Under certain circumstances, a vortex (such as illustrated in FIG. 2herein) may operate to separate laminar flow, particularly near outerportions of a cylindrically-shaped volume. Such boundary layerseparation of a compressible fluid, may operate to bring about unsteadyor turbulent flow at an upstream side of a cylindrically-shaped volume.In embodiments, such boundary layer separation operates to impede normalupstream-to-downstream flow of a compressible fluid by constricting ornarrowing an effective working area available for movement of a volumeof the compressible fluid. Such constricting or narrowing of aneffective working area available for movement of a volume ofcompressible fluid, may be understood utilizing an expressionsubstantially in accordance with:

Flow Volumeα(Diameter)²  (1)

Wherein “α” indicates proportionality in expression (1). Thus, inaccordance with expression (1), flow volume of a fan is proportional tothe square of a diameter of a channel through which a compressible fluidmay flow. Thus, in one possible example simply to illustrate theconcept, responsive to a narrowing of a cylindrically shaped volumefrom, for example, 20.0 cm to 18.0 cm (10.0%) may give rise to adecrease in fan flow volume of approximately 19.0% in accordance with anexample application of expression (1):

(20.0)² − (18.0)² = 76.0 76.0/400.0 = 0.19 =  > 19.0%

Accordingly, as can be seen by applying expression 1, narrowing orconstricting of a working area through which a compressible fluid mayflow (such as a 10.0% reduction in diameter of the working area) bringsabout a reduction in the volume of compressible fluid flow that isproportional to the square of the reduction in the diameter of the flowchannel (such as by 19.0%). Accordingly, to compensate for suchreduction flow volume of the compressible fluid, an angular velocity(e.g., fan blade speed in revolutions per minute) of the one or moreblades may be increased accordingly in order to maintain a flow volumeof the compressible fluid. Such increased angular velocity of one ormore blades of a fan may be brought about, for example, by increasingprimary power supplied to a fan in order to maintain movement of aparticular volume of compressible fluid. In other instances, a fan motoror other type of driving element may experience an increased load, whichmay also bring about an increase in power primary power supplied to afan. In other instances, to maintain a particular volume of flow of acompressible fluid, a diameter of cylindrically-shaped shroud may beincreased. However, such increases in a diameter of acylindrically-shaped shroud may bring about undesirable increases in fanfootprint, for example.

However, as described herein, to address these issues (and potentiallyothers), in particular embodiments of claimed subject matter, acylindrically-shaped shroud may comprise, for example, a vortexcirculation channel. In particular embodiments, a vortex circulationchannel may be formed within the cylindrically-shaped shroud and may besized to accept one or more blade tips or outer portions of rotating fanblades. The vortex circulation channel, which may encircle or surroundthe tip or outer portion of the one or more blades of a rotating fan,may operate to confine a vortex generated in response to rotationalmotion of the one or more blades of the fan as the blades move along thelength of the channel. Accordingly, in embodiments, a vortex generatedby rotational motion of the one or more blades of the fan may beprecluded from narrowing or constricting of a working area through whicha compressible fluid may flow. Consequently, and in accordance withexpression (1), a capacity to move a volume of a compressible fluid froman upstream side to a downstream side may be advantageously maintainedor increased without increasing primary power supplied to a fan.Confinement of a vortex generated in response to rotational motion ofone or more blades of the fan may bring about additional advantagesand/or benefits, such as bringing about a reduction in a footprint of afan shroud/fan assembly, and claimed subject matter is not limited inthis respect.

FIG. 1 is a perspective view of an example axial fan 100, wherein aplurality of fan blades rotate in a plane within a volume substantiallysurrounded by a fan shroud. In FIG. 1, cylindrically-shaped shroud 130surrounds blades 140, which operate to transport a volume of acompressible fluid from upstream side 110 to downstream side 120.Although eight of blades 140 are shown as being capable of rotationalmotion, as referenced schematically via arrow 152, in a plane about axis150, claimed subject matter is intended to embrace fans incorporatingany number of blades, such as a single blade, two blades, three blades,six blades, 10 blades, and so forth. In FIG. 1, blades 140 are depictedas being canted or tilted, such as along the length of the blade, at anangle relative to a plane of rotational motion. However, blades 140 maybe tilted at any appropriate angle, such as an angle of between 5.0° and60.0°, such as at any portion along the length of the blades 140, forexample, and claimed subject matter is not limited in this respect.

In FIG. 1, responsive to rotational motion of fan blades 140 about axis150, an increased pressure may form at downstream side 120 relative toupstream side 110. In embodiments, such increased pressure may bringabout movement of a portion of the compressible fluid from downstreamside 120 in a direction toward upstream side 110. In FIG. 1, movement ofa compressible fluid from downstream side 120 toward upstream side 110,as shown by arrows 115, may occur between gap-like regions or spacingsbetween a tip or outer portion of one or more of blades 140 and an innersurface of cylindrically-shaped shroud 130. As compressible fluidflowing through the gap-like regions meets with compressible fluidflowing from upstream side 110, a vortex may form (as shown in greaterdetail in FIG. 2), which may operate to constrict or narrow an effectiveworking area available for transporting the compressible fluid.

FIG. 2 is a schematic view of an axial fan 200, showing fan bladesrotating in a plane within a volume substantially surrounded by a shroud(such as shroud 130 of FIG. 1). In FIG. 2, shroud 220 is shown assubstantially surrounding fan blades 210 and 211 as vortices circulatefrom a downstream side to an upstream side. Responsive to rotation offan blades 210 and 211, such as in a plane perpendicular to axis 225relative to shroud 220, a compressible fluid may move from upstream side230 to downstream side 240. Responsive to movement of a volume of acompressible fluid towards downstream side 240, pressure may increase atdownstream side 240 relative to upstream side 230. In response to apressure increase, a portion of compressible fluid accumulated atdownstream side 240 may be transported back towards upstream side 230,such as through gap-like region 215 between tip portions of fan blade210 and shroud 220. As portions of the compressible fluid meet withincoming fluid from upstream side 230, the portions of the compressiblefluid may be redirected towards axis 225 and further redirected towardsdownstream side 240, thereby forming vortex 250.

Similarly, vortex 260 may also form responsive to a portion of thecompressible fluid from downstream side 240 flowing through a gap-likeregion 216 defining a spacing between a tip portion of fan blade 211 andshroud 220, as shown near the bottom of FIG. 2. In like manner, vorticesmay form between gap-like regions between additional tip portions of theblades of a fan and shroud 220. Thus, as shown in FIG. 2, a presence ofvortices, such as vortices 250 and 260, may operate to narrow orconstrict a working area through which a volume of a compressible fluidmay flow. In FIG. 2, a narrowing of a working area through which acompressible fluid may flow is indicated by bracket 270. Compressiblefluid flow lines 252 and 262, which begin near lip 222 of shroud 220 areshown as deflecting inward towards axis 225 responsive to the presenceof vortices 250 and 260.

FIG. 3 is a schematic view of an example axial fan, showing fan bladesrotating in a plane within a volume substantially surrounded by ashroud, according to an embodiment 300. In FIG. 3, shroud 320 is shownas substantially surrounding fan blades 310 and 311 as a vortexcirculation channel operates to confine a vortex. As fan blades 310 and311 rotate about axis 325 relative to shroud 320, a compressible fluidmay move from upstream side 330 to downstream side 340. Responsive tomovement of a volume of a compressible fluid towards downstream side340, pressure may increase at downstream side 340 relative to upstreamside 330. Responsive to a pressure increase, a portion of compressiblefluid accumulated at downstream side 340 may begin to move in oppositedirection towards upstream side 330, for example.

However, as a compressible fluid moves from downstream side 340 toupstream side 330, at least a fraction of the compressible fluid mayenter vortex circulation channel 335, located above blade 310 in FIG. 3,which may initiate a counterclockwise rotation of the compressible fluidwithin channel 335. In an embodiment, the fraction of the compressiblefluid may move in a counterclockwise direction defined by boundary 355of vortex circulation channel 335. After moving in a direction definedby boundary 355 of vortex circulation channel 335, the fraction of thecompressible fluid may progress to an upstream side of the vortexcirculation channel. Responsive to motion of blade 310, the fraction ofthe compressible fluid may continue moving in a counterclockwisedirection, thereby circulating within vortex circulation channel 335. Inembodiments, such circulation of the fraction of the compressible fluidwithin vortex circulation channel 335 may bring about decreased pressurewithin the channel, thereby drawing additional compressible fluid fromdownstream side 340. Accordingly, vortex circulation channel 335 mayassist in bringing about vortex 350, which may be substantially confinedwithin the circulation channel.

Likewise, as a compressible fluid moves from downstream side 340 toupstream side 330, at least a fraction of the compressible fluid mayenter vortex circulation channel 335, located below blade 311 in FIG. 3,which may initiate a clockwise rotation of the compressible fluid withinvortex circulation channel 335. In an embodiment, the fraction of thecompressible fluid may move in a clockwise direction defined by boundary355 within vortex circulation channel 335 in a curling-like motion.After moving in a direction defined by boundaries 355 of vortexcirculation channel 335, the fraction of the compressible fluid mayprogress to an upstream side of the vortex circulation channel.Responsive to motion of blade 311, the fraction of the compressiblefluid may continue motion in a clockwise direction, thereby circulatingwithin vortex circulation channel 335. In embodiments, such circulationof the fraction of the compressible fluid within vortex circulationchannel 335 may bring about a decreased pressure within the vortexcirculation channel, thereby drawing additional compressible fluid fromdownstream side 340. Accordingly, vortex circulation channel 335 mayassist in bringing about vortex 360, which may be substantially confinedwithin the circulation channel.

In like manner, vortices, such as vortices 350 and 360 may form within,and remain substantially confined within, vortex circulation channel 335as additional blades of a fan rotating relative to shroud 320 in a planeabout axis 325. Accordingly, as distinguished from the arrangement ofFIG. 2, confining vortices to within a vortex circulation channel, suchas described in connection with the confinement of vortices 350 and 360,may preclude or reduce narrowing or constricting of a working areathrough which a volume of compressible fluid may flow. Thus, as shown inFIG. 3, flow lines 352 and 362 indicate substantially laminar flowthrough at least a considerable portion of the volume defined by shroud320. In FIG. 3, an absence, or at least a reduction, of narrowing of aworking area through which a compressible fluid may flow is indicated bybracket 370. Flow lines 352 and 362, which begin near forward edge 322of shroud 320 are shown as remaining substantially parallel to indicatethe substantial confinement of vortices 350 and 360 to within a volumedefined by vortex circulation channel 335.

FIG. 4 is a schematic view of an example axial fan 400, showing fanblades rotating in a plane within a volume substantially surrounded by ashroud according to an embodiment. FIG. 4 shows confinement of a vortexwithin a circulation channel along with relative dimensional propertiesaccording to an embodiment. In the embodiment of FIG. 4, certainfeatures are exaggerated so as to illustrate, for example, radius ofblade assembly 410 (R₁) as well as a radius of curvature ofupstream-faced and downstream-faced semicircular regions of vortexcirculation channel 435 (R₂). In the embodiment of FIG. 4, upper andlower tips or outer portions of blade assembly 410 are shown withinvortex circulation channel 435 as blade assembly 410 rotates about axis425 to draw a compressible fluid from upstream side 430 to downstreamside 440. In embodiments, a ratio between the radius of blade assembly410 (as referenced via R₁) to a radius of curvature of vortexcirculation channel 435 (as referenced via R₂) may vary between 10.0:1.0and 100.0:1.0. In a particular embodiment, the ratio R₁:R₂ may be equalto about 48:1. However, claimed subject matter is intended to embraceall usable ratios of a radius of a fan blade or fan blade assembly(e.g., R₁) to a radius of curvature of a vortex circulation channel(e.g., R₂), virtually without limitation. In the embodiment of FIG. 4,vortex circulation channel 435 additionally comprises protruding edge438, located proximate with an upstream side of the vortex circulationchannel, which operates to direct flow of the compressible fluid towardsthe plane of rotation of blade assembly 410. Vortex circulation channel435 may further comprise protruding edge 439, located proximate with adownstream side of the channel, which, in cooperation with protrudingedge 438, operate to confine a vortex within circulation channel 435.

FIGS. 5A and 5B illustrate one or more fan blades that may include afin-shaped or other type of projection according to embodiments 500 and550. In FIG. 5A (embodiment 500), blades 510 include fin 520 or otherprojection, which move within a vortex circulation channel, for example,as shown by dotted lines 522 and 524. In particular embodiments, fin520, or other projection, may be positioned on an aerodynamic surface ofa blade at a predefined distance from the leading edge and proximate toa blade tip. As described in greater detail in connection with FIG. 5B(embodiment 550), presence of fin 520 may operate to reduce occurrenceof stray vortices, such as, for example, vortices indicated by arrows570 FIG. 5B that may form in response to rotation of blades 510 aboutaxis 530. Accordingly, if tip portions of blades 510, comprising fins520, traverse a vortex circulation channel, as shown by dotted lines 522at 524, vortex 350 (of FIG. 3) for example, may form exclusive of strayor parasitic vortices such as, for example, vortices indicated by arrows570 FIG. 5B. In embodiments, formation of a single vortex, such asvortex 350 within a vortex circulation channel, may bring aboutincreased flow volume of, for example, a fan operating to transport avolume of the compressible fluid from an upstream side to a downstreamside.

In FIG. 5B (embodiment 550), blade 560 is shown in detail as advancingduring nominal rotation of the blade about an axis, such as in adirection as referenced via arrow 565. Blade 560 may operate in a mannersimilar to that of blades 310 and 311 as described in FIG. 3. As blade560 of FIG. 5B advances through a medium of a compressible fluid, suchas ambient air, a volume of the compressible fluid in contact with orproximate with an aerodynamic surface of blade 560 may comprise adecreased pressure (as indicated by P↓ in FIG. 5B) relative to apressure of a volume of the compressible fluid located opposite anaerodynamic surface of blade 560 (as indicated by P↑ in FIG. 5B).Responsive to a difference in pressure, compressible fluid emanatingfrom locations opposite an aerodynamic surface of the blade may be drawntowards an aerodynamic surface of tip portion 566 of blade 560, as shownby arrows 570 in FIG. 5B. However, as the compressible fluid is drawn toa region located in contact with or proximate with an aerodynamicsurface of blade 560, the compressible fluid may encounter fin 580. Inembodiments, fin 580 operates to deflect the compressible fluid towardsa trailing edge portion of blade 560, as indicated by arrow 590. Thus,at least in particular embodiments, fin 580 may interrupt formation ofstray vortices, such as tip vortices, for example, by redirectingcompressible fluid flow drawn over a tip portion of advancing blade 560.

In FIG. 5B (embodiment 550), fin 580 comprises a length referenced via“L,” which may comprise a length of between about 25.0% and about 100.0%of the width (as referenced via W₁) of blade 560, for example, as shownschematically in FIG. 5C. However, it should be noted that in otherimplementations, fin 580 may comprise a length of less than 25.0%relative to blade width W₁ or to comprise a length of greater than100.0% of blade width W₁, and claimed subject matter is not limited inthis respect. In addition, vertical dimension H₁ of fin 580, shown inFIG. 5C, may range between about 10.0% and about 50.0% relative to bladewidth W₁. However, it should be noted that in other implementations, fin580 may comprise a vertical dimension less than 10.0% relative to bladevertical dimension H₂, or may comprise a vertical dimension greater thanabout 50% relative to blade width W₁, and claimed subject matter is notlimited in this respect.

A compressible fluid, as indicated by reference designator 576 in FIG.5B, may additionally be drawn towards an aerodynamic surface of atrailing portion of blade 560 as indicated by arrow 575 of FIG. 5Bresponsive to a pressure differential between a region located oppositean aerodynamic surface of blade 560 and a region proximate with anaerodynamic surface of blade 560. However, in embodiments, trailing edge585 of blade 560 may provide a stopping or blocking function so as torestrict or preclude a compressible fluid from colliding with a flow ofthe compressible fluid from an aerodynamic surface of blade 560, such asindicated by line 590. In particular embodiments, restrictingcompressible fluid drawn from regions located opposite an aerodynamicsurface of blade 560, may increase fan efficiency, flow volume, and/oraerodynamics of blade 560. Restricting compressible fluid drawn from aregion opposite an aerodynamic surface of blade 560 may bring aboutadditional benefits and/or advantages, and claimed subject matter is notlimited in this respect.

In particular embodiments, such as shown in FIG. 5C a portion of atrailing edge of blade 560, may comprise a width W2 of between about10.0% and about 40.0% of the width of blade 560 (W₁). However, claimedsubject matter is intended to embrace trailing edge portions of bladescomprising a width of less than 10.0% (such as 5.0%) or greater than40.0% (such as up to 100.0%) of a width of blade 560, and claimedsubject matter is not limited in this respect. In another embodiment,such as shown in FIG. 5D, fin 582 may be raised toward a trailing edgeportion of blade 565. In an embodiment, fin 582 may comprise a verticaldimension (H_(1A) in FIG. 5D) between 1.0% and 50.0% of the width ofblade 560 (W₁).

FIG. 6A is a schematic view showing fan blades rotating in a planewithin a volume substantially surrounded by a shroud. In the example ofFIG. 6A, a compressible fluid is drawn towards axial fan 600 fromvarious regions at upstream side 606, as referenced via flow lines 615.However, compressible fluid that makes contact with forward edge 622 atdiscontinuity 622A may bring about formation of vortex 624 formedproximate with a surface of forward edge 622. Accordingly, although thequarter-circle shape of forward edge 622 may operate to decreaseturbulence, a presence of discontinuity 622A may nonetheless assist increating vortex 624 and to bring about an at least semi-laminar flow ofa compressible fluid entering the axial fan of FIG. 6A. In particularimplementations, formation of vortex 624 may operate to interrupt orseparate laminar flow along forward edge 622, thus reducing volume ofcompressible fluid flow from upstream side 606 to downstream side 608,for example. In a similar manner, although not shown in FIG. 6A,vortices similar to vortex 624 may form at regions located around acircular perimeter of forward edge 622. Inlet vanes 618 may operate toalign flow, such as represented by flow lines 615, so as to increaselaminar flow through the volume defined by shroud 620.

FIG. 6B is a schematic view of a portion of an axial fan within a shroudhaving a semicircular or radiused forward edge portion according to anembodiment 625. As shown in FIG. 6B, forward edge 632 comprises a shapethat is at least approximately semicircular to permit a compressiblefluid, as indicated by flow lines 635, to wraparound forward edge 632 soas to initiate substantially laminar flow into a volume defined byshroud 630, for example. In embodiments, such laminar flow precludesformation of vortices, such as vortex 624, which may form near an upperportion of forward edge 622 of FIG. 6A. In the embodiment of FIG. 6B,arc-shaped vanes 638 may be oriented so as to guide and/or align laminarflow, thereby preventing formation of vortices as the flow wraps aroundthe reduced shroud inlet radius and/or responsive to rotational motionof the blades of blade assembly 610 as a compressible fluid flows fromupstream side 626 to downstream side 628. In particular embodiments,wraparound forward edge 632 cooperates with arc-shaped vanes 638 bringabout relatively high flow volume of compressible fluid through arelatively small inlet area. It should be noted that although forwardedge 632 is shown as comprising a substantially semicircular shapesubtending an approximately 180° angle, embodiments of claimed subjectmatter may comprise forward edges that subtend angles less than 180°,such as 135°, 150°, and so forth, or may comprise shapes that subtendgreater than 108°, such as 270°, 300°, or 360° (e.g., in which forwardand edge 632 wraps completely around to terminate at a point on shroud630).

For example, at least in particular embodiments, arc-shaped vanes 638may give rise to redirection of the flow of compressible fluid inaddition to redirection of the flow brought about by the drawing orpulling force generated by the rotational motion of the blades of bladeassembly 610. In embodiments, responsive to providing redirectingsurfaces, such as by way of a plurality of arc-shaped vanes 638, areduction in the likelihood of separation of the compressible fluid fromthe surrounding shroud may be achieved. Further, a plurality ofarc-shaped vanes 638 may additionally operate to maintain velocity andlaminar flow of the compressible fluid, such as inlet regions onsubsequent vanes near a boundary of the surrounding shroud. Arc-shapedvanes 638 operating in concert with semicircular-shaped forward edge 632may bring about additional advantages, and claimed subject matter is notlimited in this respect.

FIG. 6C is a schematic view of inlet vanes, such as those shown in FIG.6B, according to an embodiment 650. In embodiment 650, arc-shaped inletvanes 658A-658G are shown comprising airfoils having incrementallydecreasing curvatures beginning with larger curvatures toward forwardedge 652 and smaller curvatures away from forward edge 652. Accordingly,arc-shaped inlet vane 658A, which may be positioned relatively close toforward edge 652, may comprise a curvature and length greater thanarc-shaped inlet vanes 658B-658G. Arc-shaped inlet vane 658B, shown inFIG. 6C as positioned radially inward from arc-shaped inlet vane 658A isshown as comprising a curvature and length less than arc-shaped inletvane 658A. As shown in FIG. 6C, arc-shaped inlet vanes 658C, 658D, 658E,658F, and 658G comprise successively decreasing arc angles as well assuccessively reduced curvatures. In embodiments, arc-shaped inlet vanes658A-658G operate to maintain laminar flow (referenced via 655) of acompressible fluid at a first side of forward edge 652, such as region662, to a second side of inlet vanes 658A-658G, such as region 664.

FIG. 6D is a schematic view of inlet vanes, such as those shown in FIG.6B, according to an embodiment 675. As shown in FIG. 6D, arc-shapedinlet vanes 658A-658G approximate an arc shape that subtends from point680 located at the center of semicircular-shaped forward edge 678. Inparticular embodiments, such arrangement and orientation of arcshaped-inlet vanes brings about an increased ability to maintain alaminar flow of a compressible fluid at a first side of forward edge672, such as region 660A, to a second side of inlet vanes 658A-658G,such as region 660B.

FIGS. 6E and 6F represent schematic views of inlet vanes showing anincrease in fan working area according to an embodiment. In FIG. 6E,inlet vanes 688, which may be similar to inlet vanes 618 of FIG. 6A, forexample, operate to draw a compressible fluid toward a volume defined byshroud 686. As shown in FIG. 6E, shroud 686 may comprise a taper asreferenced via T. In embodiments, such taper may operate to narrow avolume through which a compressible fluid may flow. In particularembodiments, radius R₄ may comprise a value approximately in the rangeof between 5.0% and 20.0% of fan inlet dimension H₃. Taper T of FIG. 6Emay comprise a value approximately in the range of 3.0%-7.0% of faninlet dimension H₃. Accordingly, in one possible example to illustrate,assume H₃=64.77 cm (25.50 inches), 2R₄=2 (3.18) cm (2.50 inches), T=1.27cm (0.5 inch), and H₄=58.41 (23.0 inches). Accordingly, a working areaof such a fan may be computed as follows:

Fan Working Area=π×(58.41/2)²=2679.1 cm²  (2)

In FIG. 6F, inlet vanes similar to inlet vanes 658A-658B of FIG. 6Doperate to draw a compressible fluid toward a volume defined by shroud692. As shown in FIG. 6F, shroud 692 comprises a wraparound forward edgesuch as shown in FIG. 6B, which brings about laminar flow that maypreclude formation of vortices, such as vortex 624 of FIG. 6A. Inparticular embodiments, forward edge 672 of shroud 692 may be formedutilizing a smaller radius of curvature than forward edge 622 of FIG.6E. Additionally, tapering of an inner surface of shroud 692 may beunnecessary. Accordingly, in a particular embodiment, a radius (R₅) offorward edge 672 may comprise a value approximately in the range ofbetween 1.0% and 7.5% of fan inlet dimension H₅. In one example toillustrate, assume H₅=64.77 cm (25.5 inches), R₅=1.07 cm (0.42 inches),and H₆=59.94 cm (23.60 inches). Accordingly, a working area of a fan maybe computed as follows:

Fan Working Area=π×(59.94/2)²=2820.4 cm²  (3)

Thus, as evidenced by comparing the fan working area referenced by (2)with the fan working area referenced by (3), an embodiment of claimedsubject matter may bring about an approximately 5.0% increase in a fanworking area. Such an increase in fan working area may be realized as aconsequence of utilizing a wraparound forward edge, such as shown in theembodiments of FIGS. 6B, 6C, 6D, and 6F. By utilizing a wraparoundforward edge, a vortex, such as vortex 624, as shown in FIG. 6A, may beprecluded from forming, which may increase laminar flow into a volumeformed by shroud surrounding a fan blade. A wraparound forward edge maybring about additional benefits and/or advantages, and claimed subjectmatter is not limited in this respect. In one possible embodiment, useof a wraparound forward edge may reduce the need for a flange mounted toa forward portion of an axial fan, which may add approximately 2.5 cmto, for example, H₃ in FIG. 6E.

As previously mentioned herein, such as with respect to FIG. 2, in manyinstances, as one or more fan blades rotate in a plane about a centralaxis, thereby driving a compressible fluid from an upstream side of thevolume enclosed by a cylindrically-shaped shroud to a downstream side,pressure at the downstream side may increase relative to pressure at theupstream side. Accordingly, under certain circumstances, as describedwith respect to FIG. 7B-7D herein, rotating blades of a fan, accordingto particular embodiments of claimed subject matter, may utilize aprimary blade and a secondary blade located, for example, at a trailingedge of a primary blade.

FIG. 7A, which is followed by FIGS. 7B-7D, is a schematic diagramshowing velocity gradients at various points along an aerodynamicsurface of fan blade 725. FIG. 7A shows a velocity gradient formedresponsive to a compressible fluid, such as air, flowing over anaerodynamic surface of, for example, fan blade 725, as indicated byarrow 720, located at a low-pressure of fan blade 725, as referenced viaP↓, in FIG. 7A. A low-pressure side of fan blade 725 (P↓) maycorrespond, for example, to upstream side 110 of FIG. 1. At point 702 ofFIG. 7A, for example, as a distance from an aerodynamic surfaceincreases, a velocity of a compressible fluid may also increase untilreaching a constant velocity value, referenced via V_(c) in legend 715of FIG. 7A. Similarly, at additional points along an aerodynamic surfaceof fan blade 725, such as points 704, 706, 708, as a distance from theaerodynamic surface increases, velocity of the compressible fluidincreases before reaching a constant value.

However, as shown in FIG. 7A, at point 710, for example, a compressiblefluid from a side of fan blade 725 opposite an aerodynamic surface, suchas region 724, for example, may swirl around a trailing edge portion offan blade 725 as shown by arrow 716. As previously mentioned, such anincrease in pressure may be due, at least in part, to rotation of one ormore fan blades rotating in a plane about a central axis, which maythereby drive a compressible fluid from an upstream side of the volumeenclosed by a cylindrically-shaped shroud to a downstream side. In FIG.7A, a high-pressure side of fan 725 (e.g., a side opposite anaerodynamic surface of fan blade 725) referenced via P↑ may correspondto, for example, to downstream side 120 of FIG. 1. Further, as fan blade725 rotates with increasing velocity, which may operate to increasedownstream pressure in a cylindrical volume enclosed by a shroud,pressure at or near a side opposite an aerodynamic surface of fan blade725, referenced via P↑, may increase.

In FIG. 7A, as fan blade 725 advances so as to transport a volume of acompressible fluid from an upstream side to a downstream side, forexample, velocity of the compressible fluid at or proximate to atrailing edge portion of fan blade 725 may decrease to a value below0.0, which may indicate turbulent flow at, for example, point 710 of fanblade 725. Such turbulent flow, referenced via flow field 717, mayindicate flow of the compressible fluid in a direction opposite to thatof arrow 720. Responsive to oppositely-directed flow of a compressiblefluid, a decrease in a volume of the compressible fluid that may bemoved by rotation of fan blade 725 may occur. Oppositely-directed flowof compressible fluid may bring about additional undesirable effects,and claimed subject matter is not limited in this respect. It may beappreciated that turbulent flow, such as referenced via flow field 717,for example, may increase as a velocity of compressible fluid flowingover an aerodynamic surface, such as an aerodynamic surface of fan blade725, increases.

FIG. 7B is a schematic diagram showing velocity gradients at variouspoints along an aerodynamic surface of a primary blade responsive to apresence of a secondary blade according to an embodiment 750. Inembodiment 750, arrow 770 indicates flow of the compressible fluid overan aerodynamic surface of primary blade 775. Thus, at points 752, 754,756, and 758, a velocity gradient may be formed in which a velocity ofthe compressible fluid increases as a distance from an aerodynamicsurface increases. However, as shown in FIG. 7B, a secondary blade 778,which may be positioned proximate with a trailing edge of an aerodynamicsurface of primary blade 775, may bring about a directed flow of thecompressible fluid through a gap separating secondary blade 778 fromprimary blade 775 as indicated by arrow 780. Thus, swirling of acompressible fluid around a trailing edge portion of primary blade 775,as described in connection with FIG. 7A, for example, may be suppressed.In response, a velocity gradient that does not approach 0.0, or negativevalues, at point 760 (wherein point 760 corresponds to a location on atrailing edge of primary blade 775) may be formed.

Responsive to an absence of a formation of oppositely-directed flow ofthe compressible fluid, a flow volume of a fan utilizing one or more ofprimary blade 775, operating in combination with secondary blade 778,may be significantly increased without, or with only a minimal increase,in angular velocity of fan blade 775. In addition, in embodiments,utilizing one or more of primary blade 775 operating in combination withsecondary blades 778 may permit an axial fan, for example, to operateefficiently and effectively even at relatively low ranges of tangentialblade velocity and/or angular velocity. Further, as flow volume of a fanutilizing one or more of primary blade 775 and secondary blade 778increases, which may give rise to an increase in pressure at or near aside opposite to an aerodynamic surface of fan blade 775, a largervolume of a compressible fluid may be available for movement through agap separating secondary blade 778 from primary blade 775 (referencedvia arrow 780). An added benefit of an embodiment similar to that ofFIG. 7B may additionally comprise a reduction in audible noiseresponsive to turbulence created by a collision of oppositely-directedcompressible fluid, such as described with reference to FIG. 7A. Anadditional benefit of an embodiment similar to that of FIG. 7B mayadditionally comprise a possibility of reducing a number of primaryblades 775 and secondary blades 778, such as for example, from aneight-bladed fan, such as shown in FIG. 1, for example, to a six-bladedfan. Use of a secondary blade, such as secondary blade 778, for example,may bring about additional advantages in operation of an axial fan, andclaimed subject matter is not limited in this respect. Such additionaladvantages may include, for example, an increase in structural integrityof one or more blades of a fan, in which a secondary blade, which may becoupled via structural elements to a primary blade, may operate as atruss to provide structural support to a primary blade.

FIG. 7C is a schematic diagram showing various dimensions of a primaryblade and a secondary blade according to an embodiment 790. Inparticular exemplary embodiments, a width dimension of a secondaryblade, referenced via W_(sb) in FIG. 7C, may comprise between 20.0% and75.0% of the width of primary blade 775. In embodiments, a secondaryblade, such as secondary blade 778, may be disposed along the entirelength, or any portion thereof, of primary blade 775, and claimedsubject matter is not limited in this respect. In addition, a gapbetween primary blade 775 and secondary blade 778 referenced via L_(g)in FIG. 7C, may comprise between 2.0% and 100.0% of the width of primaryblade 775, although claimed subject matter is not limited in thisrespect. Thus, in particular embodiments, a gap between primary blade775 and secondary blade 778 may comprise between 2.0% and 75.0% of thewidth of primary blade 775, for example. In an embodiment, a gap betweenprimary blade 775 and secondary blade 778 may comprise approximately35.0% of the width of primary blade 775.

In embodiments, a leading edge of a secondary blade, such as secondaryblade 778, may overlap with a trailing edge portion of a primary blade,such as primary blade 775, as referenced via W_(g) in FIG. 7C. Suchoverlap, in this context, is defined as an amount, such as a percentageof primary blade width (W_(sb)) is disposed directly over (at least inthe orientation of FIG. 7C) an aerodynamic surface of secondary blade778. In embodiments, a primary blade, such as primary blade 775, forexample, may overlap a secondary blade, such as secondary blade 778, forexample, by an amount of between 0.0% and approximately 75.0%(W_(g)/W_(sb)=0.0 to 0.75), although claimed subject matter is notlimited in this respect. In an embodiment, a primary blade, such asprimary blade 775, for example, may overlap a secondary blade, such assecondary blade 778 by approximately 25.0% (W_(g)/W_(sb)˜0.25). Itshould be noted that claimed subject matter is intended to embrace anyoverlap of a primary blade with respect to a secondary blade, virtuallywithout limitation.

FIG. 7D is a schematic diagram showing possible orientation angles ofsecondary blade 778 relative to a chord line of primary blade 775according to an embodiment 795. In FIG. 7D, a chord line of secondaryblade 778 may comprise approximately 5.0° (referenced via A in FIG. 7D)in relation to chord line 796 of primary blade 775. In anotherembodiment, a chord line of secondary blade 778 may compriseapproximately 60.0° (referenced via B in FIG. 7D) in relation to chordline 796 of primary blade 775. It should be noted that claimed subjectmatter is intended to embrace any angular orientations of secondaryblade 778 in relation to chord line 796 of primary blade 775, such as2.0°, 10.0°, 30.0°, and so forth.

It may be appreciated, that at a perimeter portion, such as a tipportion, for example, of an axial fan, a tangential velocity mayapproach a relatively large value. Accordingly, at a tip portion of ablade of an axial fan, width of a primary blade and a secondary blademay approach a relatively small value while maintaining an ability tomove a relatively large volume of a compressible fluid from an upstreamside to a downstream side. Further, at a tip portion of a blade of anaxial fan, an orientation of a secondary blade may comprise a relativelysmall value, such as a value between 0.0° and, for example, 20.0°, justas an example. However, at locations along a primary fan blade closer toa central axis of rotation of an axial fan, tangential velocity of ablade of an axial fan may be significantly reduced with respect totangential velocity of a tip portion of a primary fan blade. Under suchcircumstances, an orientation angle of a secondary blade relative to achord line of a primary blade may comprise a value significantly largervalue, such as a value that approaches 35°, 40°, or even, for example,an angle of 60° or larger.

FIG. 8A is a schematic diagram showing a cross section of a fan shroud,vortex pocket, and arc-shaped inlet vanes according to an embodiment800. In FIG. 8A, a volume of the compressible fluid is shown as flowingthrough arc-shaped vanes 858. Flow lines 852, which are depicted asbeing of approximately equal length, illustrate a constant velocityprofile of a flow of the compressible fluid from upstream side 826 todownstream side 828. For clarity, one or more fan blades, which maybring about movement of a volume of compressible flow, are not shown inFIG. 8A.

FIG. 8B is a schematic diagram showing a primary and secondary blade,wherein the primary blade comprises an increasing pitch toward the bladehub, according to an embodiment 850. In the embodiment of FIG. 8B, hub890 may correspond to a location, such as toward a center region of anaxial fan, at which a primary blade and a secondary blade may attach,for example. In embodiments, the primary and secondary blades of FIG. 8Bmay advance, such as during axial rotation of the primary and secondaryblades, as referenced via arrows 891.

As shown in FIG. 8B, a primary blade, which may comprise primary bladesection 875A, may comprise a width referenced via W_(pb2), which maycorrespond to width W_(pb) of the primary blade of FIG. 7C, describedherein. Additionally, a secondary blade, which may comprise secondaryblade section 878A may comprise a width referenced by W_(sb2), which maycorrespond to width W_(sb) of the secondary blade of FIG. 7C describedherein. Further, a gap between primary blade section 875A and secondaryblade section 878A may be referenced via L_(g2), which may correspond toa gap between primary blade 775 and secondary blade 778 of FIG. 7C.Thus, the primary blade of embodiment 850 (FIG. 8B) comprises aplurality of primary blade sections, such as primary blade section 875A,875B, . . . , 875I. Additionally, the secondary blade of embodiment 850comprises a plurality of secondary blade sections, such as secondaryblade section 878A, 878B, . . . , 878I, for example.

In addition, although not shown explicitly in FIG. 8B, primary bladesection 875I comprises a width greater than W_(pb2), for example.Further, although secondary blade sections 878A, 878B, and 878I appearto comprise and least an approximately constant width (e.g.,W_(sb3)∞W_(sb2)), it is contemplated that in a number of embodiments,W_(sb3) may be greater than W_(sb2), or less than W_(sb2), and claimedsubject matter is not limited in this respect. For example, in aparticular embodiment, a secondary blade located at a perimeter, awayfrom hub 890 (e.g., W_(sb2)) may comprise a width of approximately 20.0%of a primary blade (e.g., W_(pb2)). In a particular embodiment, asecondary blade located proximate to hub 890 (e.g., W_(sb3)) maycomprise a width of approximately 75.0% of the width of a primary bladelocated proximate to hub 890, such as primary blade 878I, for example.In a particular embodiment, sections of the secondary blades, which maycomprise all of secondary blades 878A, 878B, . . . , 878I, for example,may comprise a width of approximately 50.0% of the width of a primaryblade positioned at a perimeter of the primary blade of embodiment 850.However, claimed subject matter is intended to embrace embodiments inwhich any of the sections of secondary blade comprise a width ofapproximately 20.0% of a primary blade to a width of approximately 75%of the primary blade.

As shown in FIG. 8B, primary blade sections closer to hub 890, such as,for example, primary blade section 875I, a blade pitch may comprise amuch larger angle, such as an angle between about 30.0° and about 60.0°,for example, than a blade pitch more distant from hub 890. In particularembodiments, such adjustment in blade pitch may bring about constantvelocity flow of a compressible fluid, such as shown in FIG. 8A. Toillustrate, as primary blade sections 875A, . . . , 875I and secondaryblade sections 878A, . . . , 878I rotate in a plane at a particularangular velocity (revolutions/minute) about hub 890, primary bladesection 875A and secondary blade section 878A may comprise a highertangential velocity (meters/second) than, for example, primary bladesection 875I and secondary blade section 878I, for example. Accordingly,an increased pitch of primary blade section 875I and secondary bladesection 878I, relative to primary blade section 875A and secondary bladesection 878A, respectively, may bring about movement of a substantiallyconstant volume of compressible fluid between, for example, acombination of blade sections 875A/878A compared to a combination ofblade sections 875I/878I.

FIG. 8C provides a diagram showing a numerical example utilized indetermining, or at least estimating, blade pitch of sections of theprimary and secondary blades of FIG. 8B according to an embodiment 895.In a nonlimiting example, just to illustrate a sample computation ofpitch angle of primary and secondary blade sections, the followingassumptions are made:

-   -   Blade Length: 45.72 cm (18.0 inches)    -   Desired Air Velocity: 1097.28 meter/min. (3600 feet/min.)    -   Desired Fan Speed: 3000.0 revolutions/min.        Thus, in a nonlimiting embodiment, to compute a blade pitch        angle for a primary blade section immediately adjacent, for        example, to a fan blade hub, such as primary blade section 875I        and secondary blade section 878I of FIG. 8B, the vector diagram        892 of FIG. 8C may be utilized. In vector diagram 892, a desired        air velocity of 1097.28 meter/min. may form a        vertically-oriented vector. To form the horizontally-oriented        vector of diagram 892, at a point near a fan blade hub, such as        at a distance of 7.62 cm (0.25 feet) from a central axis of        rotation and expression substantially in accordance with        expression (4) may be utilized:

3000.0 rev./min.×7.62 cm×2π=143,634.0 cm/min.=1436.34 meter/min.  (4)

Thus, in accordance with vector diagram 892, the blade pitch angle for aprimary and/or secondary blade sections, such as primary blade section875I and secondary blade section 878I, of FIG. 8B for example, which maybe positioned approximately 7.62 cm from a central axis of rotation ofhub 890 may comprise an angle having a tangent (e.g., tan⁻¹ of(1097.28/1436.34)) or 37.38° (tan⁻¹ (1097.28/1436.34)=37.38°).

Likewise, continuing with a nonlimiting embodiment, to compute a bladepitch angle for a primary blade section located near a perimeter of afan blade hub, such as primary blade section 875A and secondary bladesection 878A of FIG. 8B, the vector diagram 894 of FIG. 8C may beutilized. In vector diagram 894, a desired air velocity of 1097.28meter/min. may form a vertically-oriented vector. To form thehorizontally-oriented vector of diagram 894, at a point away from fanblade hub 890, such as at a distance of 22.86 cm (9.0 inches) from acentral axis of rotation and expression substantially in accordance withexpression (4) may be utilized:

3000.0 rev./min.×22.86 cm×2π=430,900.0 cm/min.=4309.01 meter/min.  (5)

Thus, in accordance with vector diagram 894, the blade pitch angle for aprimary and/or secondary blade section, such as primary blade section875A and secondary blade section 878A, of FIG. 8B for example, which maybe positioned approximately 22.86 cm from a central axis of rotation ofhub 890 may comprise an angle having a tangent (e.g., tan⁻¹) of1097.28/4309.01 or 14.29° (tan⁻¹ (1097.28/4309.01)=14.29°).

Accordingly, utilizing vector diagrams 892 and 894 of FIG. 8C andexpressions (4) and (5) pitch angles of primary blade sections andsecondary blade sections may be computed. Although the preceding examplecomputes pitch angles for primary and secondary blade sectionspositioned nearby hub 890 and at a perimeter (e.g., away from hub 890)additional vector diagrams similar to 892 and 894, as well as one ormore of expressions (4) and (5), may be utilized to compute pitch anglesfor additional sections of the primary and secondary blades of FIG. 8B.It should be noted that although a specific example has been utilized,such as a blade length of 45.72 cm, a desired air velocity of 1097.28meter/min., and a desired fan speed of 3000.0 revolutions/min., claimedsubject matter is intended to embrace a wide variety of blade lengths,desired air velocities, desired fan speeds, and other performanceparameters, virtually without limitation.

It should also be noted that although primary blade section 875I hasbeen described as positioned approximately 7.62 cm from a central axisof rotation of hub 890, in particular embodiments, it may beadvantageous to reduce a cross-sectional area of hub 890. Inembodiments, reduction of a cross-sectional area of hub 890 may operateto increase fan working area, as described in relation to expressions(2) and (3). For example, in accordance with expression (6) a FanWorking Area may be decreased by cross-sectional area occupied by a fanhub, such as hub 890 of FIG. 8B, as follows:

(Fan Working Area)_(Effective)=(Fan Area)−Hub Area  (6)

Accordingly, an effective Fan Working Area (e.g., (Fan WorkingArea)_(Effective)) of expression (6), may correspond to across-sectional area computed utilizing a tip-to-tip diameter of theblades of a fan, and wherein the Hub Area of expressions (6) comprises across-sectional area of the hub to which one or more blades of a fan mayattach. Thus, in accordance with expression (6), an effective FanWorking Area of 2500.0 cm², computed utilizing the tip-to-tip diameter,may be significantly reduced by the presence of a hub having a radiusof, for example, 4.0 cm, as computed substantially in accordance withexpression (7), below:

$\begin{matrix}\begin{matrix}{\left( {{Fan}\mspace{14mu} {Working}\mspace{14mu} {Area}} \right)_{Effective} = {{2500.0\mspace{14mu} {cm}^{2}} - {\pi \left( {4.0\mspace{14mu} {cm}} \right)}^{2}}} \\{= {2450.0\mspace{14mu} {cm}^{2}}}\end{matrix} & (7)\end{matrix}$

Accordingly, embodiments of claimed subject matter may operate toadvantageously reduce a cross-sectional area of a hub, such as hub 890,to which one or more fan blades may attach. Further, as a hub to whichfan blades may attach is reduced in cross-sectional area, a pitch angleof one or more blades of a fan may be adjusted (e.g., increased),utilizing, for example, expressions (4) and (5). Such increases in pitchangle of primary and/or secondary blades, in addition to reducing across-sectional area of a hub to which fan blades may attach, mayprovide a constant velocity profile of a flow of the compressible fluidfrom an upstream side (e.g., 826 of FIG. 8A) to a downstream side (e.g.,828 of FIG. 8A).

It should additionally be noted that although the example of FIG. 8B andFIG. 8C have utilized a pitch angle of a secondary blade section equalto that of a pitch angle of a primary blade section, such as primaryblade section 875I and secondary blade section 878I comprising a pitchangle of 37.38°, one or more secondary blade sections may be angled withrespect to a corresponding primary blade section. Thus, in accordancewith FIG. 7C (embodiment 795) a secondary blade section may comprise anangle of between approximately 5.0° and 60.0° with respect to a chordline of a primary blade section.

It should further be noted that at a perimeter portion of a primaryblade, such as primary blade section 875A, for example, tangentialvelocity may comprise a relatively high value, which may bring about arelatively high value of lift generated by primary blade section 875A.Responsive to a relatively high value of lift, a relatively narrow blade(e.g., relatively small value for W_(pb2)) oriented at a relativelysmall pitch angle, such as approximately 14.0°, just as an example, maybe capable of moving a significant volume of a compressible fluid froman upstream side of an axial fan to a downstream side, for example.Additionally, a relatively narrow section of a secondary blade, such assecondary blade section 878A, may also comprise a relatively narrowwidth (e.g. relatively low W_(sb2)). Further, a perimeter portion of asecondary blade, such as secondary blade section 878A, for example, maycomprise a relatively lower orientation angle, such as an angle between1.0° and 20.0° relative to a chord line primary blade section.

However, for sections of primary blade 875, which may be located closerto hub 890, such as primary blade section 875I, a tangential velocitymay approach a relatively low value, which may give rise to relativelylow values of lift compared to, for example, primary blade section 875A.Accordingly, as described in reference to FIG. 8B, primary bladesections located proximate with hub 890 may comprise a relatively largewidth and may be oriented at a relatively high pitch angle, such asapproximately 37.0°, just to name an example, so as to maintain acapability to move a particular volume of a compressible fluid from anupstream side to a downstream side of an axial fan, for example. Thus,it can be appreciated that in embodiments, use of a secondary bladesection, such as secondary blade section 878I, may assist in bringingabout significant lift, and, consequently, significant movement of thecompressible fluid. Under such circumstances, and potentially others,use of a secondary blade, as exemplified by secondary blade section878I, may provide particular advantages in maintaining laminar flow andrestricting movement of the compressible fluid from a high-pressure side(e.g., a side opposite an aerodynamic surface) of primary blade 875 to alow-pressure side (e.g., an aerodynamic surface) of primary blade 875.

It should be further noted that although the primary and secondaryblades of the embodiment of FIG. 8B (embodiment 850) comprise nineprimary and secondary blade sections, claimed subject matter is intendedto embrace primary and secondary blades comprising any number of primaryand secondary blade sections. Accordingly, claimed subject matter mayembrace primary and secondary blades comprising fewer than ninesections, such as two sections, three sections, four sections, etc., aswell as primary and secondary blades comprising greater than ninesections, such as 10 sections, 11 sections, and so forth, virtuallywithout limitation.

In the present patent application, terms such as “over” and “under” areunderstood in a similar manner as the terms “up,” “down,” “top,”“bottom,” “upward,” “downward,” and so on, as previously mentioned.These terms may be used to facilitate discussion, but are not intendedto necessarily restrict scope of claimed subject matter. For example,the term “over,” as an example, is not meant to suggest that claim scopeis limited to only situations in which an embodiment is right side up,such as in comparison with the embodiment being upside down, forexample. Thus, if an object, as an example, is within applicable claimscope in a particular orientation, such as upside down, as one example,likewise, it is intended that the latter also be interpreted to beincluded within applicable claim scope in another orientation, such asright side up, again, as an example, and vice-versa, even if applicableliteral claim language has the potential to be interpreted otherwise. Ofcourse, again, as always has been the case in the specification of apatent application, particular context of description and/or usageprovides helpful guidance regarding reasonable inferences to be drawn.

Unless otherwise indicated, in the context of the present patentapplication, the term “or” if used to associate a list, such as I, J, orK, is intended to mean I, J, and K, here used in the inclusive sense, aswell as I, J, or K, here used in the exclusive sense. With thisunderstanding, “and” is used in the inclusive sense and intended to meanI, J, and K; whereas “and/or” can be used in an abundance of caution tomake clear that all of the foregoing meanings are intended, althoughsuch usage is not required. In addition, the term “one or more” and/orsimilar terms is used to describe any feature, structure,characteristic, and/or the like in the singular, “and/or” is also usedto describe a plurality and/or some other combination of features,structures, characteristics, and/or the like. Likewise, the term “basedon” and/or similar terms are understood as not necessarily intending toconvey an exhaustive list of factors, but to allow for existence ofadditional factors not necessarily expressly described.

While there has been illustrated and/or described what are presentlyconsidered to be example features, it will be understood by thoseskilled in the relevant art that various other modifications may be madeand/or equivalents may be substituted, without departing from claimedsubject matter. Additionally, many modifications may be made to adapt aparticular situation to teachings of claimed subject matter withoutdeparting from the central concept(s) described herein. Therefore, it isintended that claimed subject matter not be limited to particularexamples disclosed, but that such claimed subject matter may alsoinclude all aspects falling within appended claims and/or equivalentsthereof.

What is claimed is:
 1. A fan shroud at least partially surrounding oneor more blades of a fan, the fan shroud comprising: a vortex circulationchannel, formed within the fan shroud, sized to accept a tip portion ofone or more blades of the fan during rotational motion of the one ormore blades of the fan, the vortex circulation channel shaped to confinea vortex generated near the tip portion of the one or more blades of thefan during the rotational motion of the one or more blades of the fan.2. The fan shroud of claim 1, wherein the vortex circulation channelcomprises at least one protruding edge disposed at an upstream directionrelative to a plane of the rotational motion of the one or more bladesof the fan.
 3. The fan shroud of claim 1, wherein the vortex circulationchannel comprises at least one protruding edge disposed at a downstreamdirection from a plane of the rotational motion of the one or moreblades of the fan.
 4. The fan shroud of claim 1, wherein the confinedvortex of the vortex circulation channel operates to avoid impeding ofthe generated vortex into a working area defined by the shroud.
 5. Thefan shroud of claim 1, wherein the confined vortex of the vortexcirculation channel operates to substantially eliminate boundary layerseparation in an upstream direction or in a downstream directionrelative to a plane of the rotational motion of the one or more bladesof the fan.
 6. The fan shroud of claim 1, wherein the one or more bladesof the fan are capable of moving a volume of a compressible fluid froman upstream side to a downstream side relative to a plane of therotational motion of the one or more blades of the fan.
 7. The fanshroud of claim 1, wherein the vortex circulation channel comprises anat least approximately semicircular profile in an upstream direction ofa plane of the rotational motion of the fan.
 8. The fan shroud of claim7, wherein the ratio between a radius of a blade of the fan to acurvature of a semicircular portion of the vortex circulation channelcomprises a value of between 10.0:1.0 and 100.0:1.0.
 9. The fan shroudof claim 1, wherein the vortex circulation channel comprises an at leastapproximately semicircular profile in a downstream direction of a planeof the rotational motion of the fan.
 10. The fan shroud of claim 1,wherein the shroud comprises a wraparound forward edge, the wraparoundforward comprising a radius of curvature of between about 2.0% and 5.0%of the radius of an area of an upstream side of the one or more bladesof the fan.
 11. A fan shroud and blade assembly, comprising: one or moreblades to move rotationally in a plane; and a shroud, at least partiallyenclosing the one or more blades of the fan, the shroud comprising avortex circulation channel formed on and sized to accept a tip portionof at least one of the one or more blades during rotational motion ofthe one or more blades of the fan, the vortex circulation channel toform a confined vortex at least partially in response to movement of thetip portion of the at least one of the one or more blades, and at leastpartially in response to a spacing between the tip portion of at leastone of the one or more blades and the fan shroud.
 12. The fan shroud andblade assembly of claim 11, wherein the shroud operates to direct a flowof a compressible fluid through the one or more blades, and wherein theconfined vortex is formed from the compressible fluid during therotational motion of the one or more blades.
 13. The fan shroud andblade assembly of claim 11, wherein the vortex circulation channeladditionally comprises at least one protruding edge disposed in anupstream direction relative to a plane of the rotational motion of theone or more blades.
 14. The fan shroud and blade assembly of claim 13,wherein the vortex circulation channel additionally comprises at leastone protruding edge disposed in a downstream direction from the plane ofrotational motion of the one or more blades.
 15. The fan shroud andblade assembly of claim 11, wherein the confined vortex of the vortexcirculation channel operates to substantially eliminate boundary layerseparation in an upstream direction or in a downstream direction,relative to the one or more blades, during rotational motion of the oneor more blades.
 16. The fan shroud and blade assembly of claim 11,wherein at least a portion of the vortex circulation channel comprisesan approximately semicircular profile having a radius of curvature ofbetween 1/10 and 1/100 of the radius of the one or more blades.
 17. Asystem to move a volume of a compressible fluid, comprising: a shroud tosubstantially surround one or more blades of a fan; and a vortexcirculation channel formed within the shroud to accept a portion of atleast one of the one or more blades of the fan during rotational motionof one or more blades of the fan, the vortex circulation channel to forma vortex to circulate a portion of the compressible fluid, the vortex toavoid interference with a working area defined by the shroud.
 18. Thesystem of claim 17, wherein the vortex circulation channel is formedwithin the shroud and sized to accept a portion of all of the blades ofthe fan during rotational motion of the blades of the fan.
 19. Thesystem of claim 17, wherein the vortex circulation channel comprises afirst approximately semicircular-shaped region at an upstream side ofthe blades of the fan and a second semicircular-shaped region at adownstream side of the blades of the fan.
 20. The system of claim 19,wherein one or more of the first approximately semicircular-shapedregion and the second semicircular-shaped region comprises a profilehaving a radius of curvature of between 1/10 and 1/100 of the at leastone of the one or more blades of the fan.